Rivers are vital ecosystems that support aquatic and terrestrial biodiversity and several ecosystem services, including food, water, culture, and recreation. After centuries of building dams on rivers across the world, dam removal projects are now on the rise due to obsolescence, reservoir sedimentation, insufficient return on investment, or river restoration and conservation priorities. Most dam removal projects have focused on smaller structures (< 10 m in structural height), but larger structures have also started to be removed in increasing numbers as practitioners, river managers, conservationists, and the public have gained more experience with the practice. Recent estimates suggest that only a small fraction of dam removals have been scientifically studied, and include mostly small dams and short time scales. Documenting the long-term ecological outcomes of large dam removal (i.e. >10 m tall) represents a new frontier in dam removal research: projects are more recent and provide an opportunity to understand the complex ecological changes that occur with these transformative restoration projects. Here, we aim to collate a diverse array of papers on long-term dam removal research projects involving larger dams (>10 m) to synthesize the issues, outcomes, tools, and experimental designs used to study large dam removal projects from physical, biological, and ecological perspectives. With this collection, we aim to showcase diverse global projects on ecosystem responses to large dam removal; collect perspectives from different disciplines, fields, and geographies; and synthesize the current state of knowledge in this area. We expect that this Research Topic will be informative to ongoing, long-term ecological restoration and monitoring projects related to dam removal as well as to upcoming large dam removal projects. We welcome contributions from all disciplines addressing the physical, ecological, and ecosystem responses to large-scale dam removal. Contributions could include original research in a specific discipline or area, case studies, or synthesis papers that address one or more of these topics in a transdisciplinary approach. Contributors could address any of the following major topics as related to outcomes of large dam removal, alone or in combination: Freshwater, estuarine, and marine aquatic biota; River and reservoir geomorphology; Terrestrial and riparian vegetation; Wildlife; Sedimentation; and Modelling. We would like contributors to highlight key results in their area of study, cross-disciplinary insights, and lessons learned that could inform ongoing monitoring and research efforts in current projects as well as upcoming large dam removals.